Suppression of corrosion



Patented Apr. 24, 1951 SUPPRESSION OF CORROSION Cecil Phillips, Jr.,Baytown, Tex., assignor to Standard Oil Development Company, Elizabeth,N. 3., a corporation of Delaware No Drawing. Application June 20, 1947,Serial No. 756,111

Claims. 1

This invention is directed to a method for suppressing the corrosion ofcopper-containing alloys in the presence of ammonia. Specifically, it isdirected to the prevention of corrosion of copper alloys in aqueoussolutions containing ammonia.

In many operations it is often desirable to use various types ofequipment (tanks, heat exchanger and condenser tubes, valves, lines,etc.) constructed of or containing copper alloys for handling solutionsor gases containing ammonia. Such equipment usually suffers from severecorrosion of the copper alloys due to the chemical dissolution of thecopper by the ammonia. The rapid destruction of the copper alloys incontact with solutions or vapors containing ammonia is believed to bedue to the formation of highly soluble copper-ammonium complex ions. Thepresence of oxygen is necessary for the formation of the solublecopper-ammonium ions.

As a result of the corrosive action of ammoniacal solutions on copper,the employers of ammonia, such as the petroleum refiner, must exerciseextreme care in selection of suitable alloys for his processingequipment. Thus, where ammonia is to be used, copper alloys are avoided.However, as mentioned before, various services require the-use of copperalloys on account of other corrosive fluids being encountered. Thus, thecorrosive action of carbon dioxide in steam makes nearly mandatory theemployment of copper alloys such as alloys of copper, zinc, and tin inheat exchange equipment using corrosive steam as the heat transfermedium. Thus, when ammonia is employed in this type of equipment, rapidattack of the copper alioy may be sufiered even though the ammonia mayprevent attack of ferrous metals by other components travelling throughthe equipment. Ammoniacal solutions are also widely used in solventextraction of hydrocarbons. Here, again the petroleum refiner must guardagainst allowing the solutions to contact copper bearing surfaces. Theaforementioned corrosion reaction generally occurs at atmospherictemperature and pressure. It is believed that higher temperatures andpressures may accelerate this reaction.

It is, therefore, the main object of the present invention to provide aprocess whereby the deterioration of copper alloys in the presence ofammonia is substantially eliminated.

Another object of the invention is to provide a method whereby copperalloys may be employed in services where they are exposed to ammoniacalsolutions.

' ammoniacal solutions.

The objects of the present invention are achieved by maintaining incorrosive ammoniacal solutions in contact with copper and its alloys acorrosion inhibiting amount of a halogen acid.

Briefly, the present invention involves the addition to corrosiveammoniacal solutions in contact with copper-containing metals of aquantity of a halogen acid in the range between 0.05 and 5% by weight ofthe ammoniacal solution. The halogen acid may be hydrochloric acid,hydrobr-omic acid, hydroiodic acid, or hydrofluoric acid.

The mechanism by which the halogen acid is effective in preventing thecorrosion of copper alloys by ammonia is not understood, but it isbelieved to involve the formation of a very thin protective film on themetal. This hypothesis is based on the fact that the halogen acid isemployed in amounts insuflicient to neutralize the Therefore, some otherexplanation of the beneficial aspects of the invention is necessary. Itis understood, of course, that I do not wish to bind myself to anytheory offered as an explanation of the benefiicial effect.

An advantage of the process of the present invention, irrespective ofthe prevention of corrosion of copper and its alloys, is the ability touse existing equipment in which copper and its alloys are present inprocesses involving the use of ammonia.

In order to illustrate the beneficial aspects of this invention,copper-containing metal copper, 29% zinc, and 1% tin) was immersed inaqueous solutions of ammonia. These tests were in progress for 24 hoursat room temperature and atmospheric pressure. Air was bubbled throughthe ammonia solutions throughout the tests. These tests were repeatedunder identical conditions with small amounts of hydrofluoric acid addedto the aqueous solutions of ammonia. Results obtained in these tests areshown in the following table:

It will be observed from the data presented in the foregoing table thatthe addition of a small amount of hydrofluoric acid effects a markedreduction in the tendencies of aqueous solutions of ammonia to corrodecopper-bearin alloys.

The present invention has utility in inhibiting the corrosive eflects ofsolutions of ammonia in water in the presence of oxygen but is alsoapplicable to inhibiting the corrosive effects of other ammoniacalsolutions. For example, solutions of ammonium acetate readily dissolvecopper and copper bearing metals. Maintenance of the required amount ofhalogen acid will effec.- tively inhibit the corrosiveness of suchsolutions to copper surfaces.

The nature and objects of the present invention having been fullydescribed and illustrated, what I wish to claim as new and useful and tosecure by Letters Patent is:

1. A method for reducing the corrosive action of a corrosive basicsolution including ammonia, water and oxygen to apparatus adapted tocontain corrosive fluids and having a corrodible copper-containingsurface in contact with said solution which comprises introducing intosaid solu tion an amount of a halogen acid sufiicient to'inhibit thecorrosion thereof but insufficient to neutralize the solution.

2. A method in accordance with claim 1 in.

which the amount of halogen acid is in the range between 0.05% and 5% byweight of the corrosive solution.

3. A method in accordance with claim 1 in which the halogen acid ishydrofluoric acid.

4. A method in accordance with claim 1 in which the halogen acid ishydrochloric acid.

5. A method in accordance with claim 1 in which the halogen acid. ishydrobromic acid.

CECIL PHILLIPS, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,994,702 Harris Mar. 19, 19352,024,680

Curtis Dec. 17, 1935 OTHER REFERENCES

1. A METHOD FOR REDUCING THE CORROSIVE ACTION OF A CORROSIVE BASICSOLUTION INCLUDING AMMONIA, WATER AND OXYGEN TO APPARATUS ADAPTED TOCONTAIN CORROSIVE FLUIDS AND HAVING A CORRODIBLE COPPER-CONTAININGSURFACE IN CONTACT WITH SAID SOLUTION WHICH COMPRISES INTRODUCING INTOSAID SOLUTION AN AMOUNT OF A HALOGEN ACID SUFFICIENT TO INHIBIT THECORROSION THEREOF BUT INSUFFICIENT TO NEUTRALIZE THE SOLUTION.